How to plot the difference between two graphs..

hi everyone..
i am doing my project on comparing two ECG signals and narrowing down the abnormalities in the another. I am having many difficulties in proceeding with this project. I am generating a normal and abnormal ecgs using ecg .txt files.
I ahve done many projects in image processing and i am have even done many projects in converting an image into binaries and subtracting them.But in these case i am unable to proceed any further . And i need all the help in the wotld since i have no team in these project.Thank you in advance

what have you tried so far? any sample code you have written you can share?
My understanding is that you want to plot the difference of two ECG signals, is that right? Can you clarify what you are trying to do?